This invention relates to telecommunication equipment that provides voice lines as well as digital and data service lines, and more particularly to plain old telephone service (POTS) lines for high speed data service.
In the United States subscribers are commonly provided with telephone services known as plain old telephone services (POTS). Such services include providing conventional dial tone and automated dialing features, including the use of dual frequency tone signaling to communicate dialed number information. Additional modem telephone features include conferencing, call waiting, incoming caller identification and other commercially available features.
Subscribers utilize a POTS line to carry conventional voice or data signals via the public switch telephone network. Modems are currently available which advertise data communication rates up to 56 Kilobits (Kb) per second over POTS lines. However, POTS lines have a limited maximum data rate as a result of the terminating circuitry at the central office.
For higher data rates than are supported by POTS lines, subscribers in the United States can lease special subscriber lines from their telephone providers. Such higher speed lines utilize different terminating circuitry at the central office to accommodate higher data rates. There are many different types of high speed digital subscriber line (XDSL) services such as asymmetrical digital subscriber line (ADSL), high bit rate digital subscriber line (HDSL), high bit rate digital subscriber line-2 (HDSL-2), rate adaptive digital subscriber line (RDSL), symmetric digital subscriber line (SDSL), very high speed digital subscriber line (VDSL), ADSL-lite, and other similar high speed digital services. Additionally, there are other non-digital high speed transmission techniques.
As an example, the known asynchronous digital subscriber line (ADSL) technique which is supported by available equipment provides a significantly higher data rate to a subscriber over a POTS subscriber line. Of course, the ADSL service requires proper terminating equipment at the central office and at the consumer premise to accommodate the greater throughput capabilities, i.e. data rates.
FIG. 1 illustrates available services in the United States to subscribers using conventional two-wire copper loops. Equipment to the right of the dashed line 100 represents customer premise equipment (CPE). Equipment to the left of the dashed line. 100 represents central office line termination equipment. A POTS line interface 102, also known as a line card, provides an interface between digital incoming and outgoing communication lines 104 and 106, and analog signals carried on subscriber line 108. For example, lines 104 and 106 may carry 64 Kb per second pulse coded modulation (PCM) signals representative of analog information received from and transmitted to line 108. A main distribution frame (MDF) 110 is used to interconnect a plurality of incoming subscriber lines to various terminating equipment at the central office. In this example, line 108 is connected through a POTS splitter 112 and MDF 110 to subscriber line 114. A conventional telephone instrument 116 at the site of the consumer is connected through a POTS splitter 118 to subscriber line 114.
FIG. 1 also illustrates another service to the subscriber which provides a high speed data capability. An XDSL interface circuit 120 provides an interface between the central office and a subscriber for terminating the receiving data at rates up to several megabits per second. Lines 122 and 124 provide inbound and outbound digital data communications, representative of information to and from the subscriber, carried on line 126. Line 126 is connected via POTS splitter 112 and MDF 110 to subscriber line 114. An XDSL interface 128 provides an interface between conventional digital data, communicated with a personal computer 130, and XDSL analog format signaling communicated on line 132. The POTS splitter 118 couples the XDSL signal between XDSL interface 128 and subscriber line 114. The advantage to the user is that the XDSL facilities support a substantially higher data rate than would be available if the subscriber utilized communications terminated via the POTS line interface 102.
The POTS splitter 112 combines the high frequency XDSL signals and low frequency POTS signals into a new combined communication signal. The POTS splitter 118 performs the reverse operation of the POTS splitter 112 and outputs a high frequency XDSL signals and low frequency POTS signals from the combined communication signal.
A disadvantage in such conventional systems is that POTS splitters are needed to separate the XDSL and POTS signals. POTS splitters take up a lot of room in the central office offices were space is valuable. Using the 0-4 kHz band for POTS and the 4-30 kHz band for POTS splitters results in only 64 kbps of information in 30 kHz of bandwidth. This is very inefficient use of bandwidth. It is even more problematic because the low bandwidths of a telephone loop are the best frequencies to be used by XDSL technologies since these frequencies have the lowest loss and have the least amount of interference. An alternative suggested by others is to use two copper pairs for each customer, one pair for POTS and one pair for XDSL. This is inefficient use of copper pairs.
The above problems are solved and a number of technical advances are achieved in the art by implementation of a system and method that allows an all digital communication system with a life line.
In accordance with the invention, a method of telephonic signaling in a communication system between a central office and a remote consumer premises equipment (CPE) interface, located at a subscriber premises, in which the communication system supports both plain old telephone service (POTS) and high speed data services is described. The method comprises the steps of transforming an analog POTS signal to a digital POTS signal, and combining the digital POTS signal with a high speed data signal into a combined digital signal which preferably has a single communication spectrum. In the case of a power failure, the method further includes the steps of identifying the occurrence of a power failure at a remote CPE interface, and establishing a life line communication path from the central office to the remote CPE interface in response to the power failure.
Also in accordance with the invention, a communication system that supports both POTS and high speed data services between a remote CPE interface, located at a subscriber premises, and a central office is described. The system comprises an analog to digital converter for transforming an analog POTS signal to a digital POTS signal, and a combiner circuit for combining the digital POTS signal with a high speed data signal into a combined digital signal which preferably has a single communication spectrum. In the case of a power failure, the system further includes a power detector for identifying the occurrence of a power failure at the remote CPE interface, and means for establishing a life line communication path from the central office to the remote CPE interface in response to the power failure.